1. Field of the Invention
The present invention relates to a piezoelectric vibrator that vibrates due to the application of voltage to a piezoelectric element, a method for adjusting this piezoelectric vibrator, a piezoelectric actuator that includes this piezoelectric vibrator, a timepiece, and an electronic device.
2. Description of the Related Art
In conventional practice, piezoelectric vibrators that use piezoelectric elements have been used in oscillators and actuators and the like in electronic circuits. In such piezoelectric vibrators, the characteristic frequency is determined by the characteristics and dimensions of the material, but the characteristic frequency in each individual vibrator must be adjusted because of the tendency of the characteristics of the piezoelectric material to be nonuniform, and because of the occurrence of errors in the working dimensions of the piezoelectric vibrators.
One known method of adjusting the characteristic frequency is a method of sequentially cutting off pieces of a rectangular piezoelectric element several dozen microns at a time from the end in the length direction with a laser (Prior Art 1). In other words, the characteristic frequency is adjusted by reducing the length of the piezoelectric element.
Another known practice is to adjust the characteristic frequency by coating the piezoelectric vibrator with paint (Prior Art 2). In this method, the position where the paint is applied and the amount applied are calculated based on the determined resonance frequency of the piezoelectric vibrator, and paint is repeatedly applied to the vibrator by a paint ejecting device until a specific resonance frequency is achieved.
In actuators that include a piezoelectric vibrator, part of the piezoelectric vibrator describes an elliptical trajectory consisting of both longitudinal vibration and bending vibration, and when the driven object is brought into contact with this elliptically moving portion and is driven, the characteristic frequencies of both the longitudinal vibration and bending vibration must be adjusted to reach a specific relationship in order to drive the object at a high efficiency while using the resonance at both the longitudinal vibration and the bending vibration. In view of this, it has been proposed that the difference in resonance frequencies of longitudinal vibration and bending vibration be adjusted by removing the frequency-adjusted portion provided to the outer periphery of the cylindrical vibrator and reducing the diameter of the vibrator by cutting, polishing, dissolving, or the like (Prior Art 3).
[Prior Art 1] Japanese Patent Application Laid-Open No. 6-204778 ([0018]-[0020], FIG. 1)
[Prior Art 2] Japanese Patent Application Laid-Open No. 10-32445 ([0011], FIG. 1)
[Prior Art 3] Japanese Patent Application Laid-Open No. 10-146070 ([0093], FIGS. 1 and 3)
However, with a method for varying the dimensions of the vibrator by cutting off pieces of the piezoelectric element as described in Prior Art 1, a large amount of energy is required, and the Q value and other such vibration characteristics may degrade due to the power or heat applied to the piezoelectric vibrator. Also, the cycle time increases because time is required to cut off pieces of the piezoelectric element. Furthermore, since many steps are required for adjustment and it is difficult to cut the material from the front side of the piezoelectric element irradiated with a laser beam to the reverse side with accurate dimensions, problems are encountered in which the characteristic frequency cannot necessarily be adjusted to the specified range and the amount of adjustment is nonuniform.
In Prior Art 3, problems are encountered with degradation in the vibration characteristics, increases in the cycle time, and nonuniformities in the adjusted amounts, similar to Prior Art 1. Particularly, it is difficult to drive the piezoelectric actuator in a stable manner because the characteristic frequencies of both longitudinal vibration and bending vibration must be maintained in order to obtain the desired elliptical trajectory, and the vibration characteristics are extremely nonuniform if the characteristic frequencies are even slightly nonuniform. This nonuniformity in the vibration characteristics poses a crucial problem, particularly in vibrators for low output.
In the method in Prior Art 2, it is difficult to control the amount of paint ejected, and therefore the amounts of paint are nonuniform among different piezoelectric vibrators, and the adjustment results have so far been unsatisfactory. Moreover, since the vibration characteristics may degrade with a greater amount of paint, problems have been encountered in that the amount of paint is limited and the characteristic frequencies can only be adjusted within an extremely small range.
In view of such problems, an object of the present invention is to provide a piezoelectric vibrator, a method for adjusting a piezoelectric vibrator, a piezoelectric actuator including a piezoelectric vibrator, a timepiece, and an electronic device, wherein the adjusted amounts of the characteristic frequencies can be ensured with little reduction in the vibration characteristics, the characteristic frequencies can be reliably adjusted by reducing nonuniformities in the adjusted amounts of the characteristic frequencies, and individual differences pertaining to the characteristic frequencies can thereby be eliminated, all with a simple configuration.